Expression of coxsackievirus and adenovirus receptor (CAR)-Fc fusion protein in Pichia pastoris and characterization of its anti-coxsackievirus activity

Human Coxsackie- and adenovirus receptor is a putative target of neutrophil elastase-mediated shedding

Background

During viral-induced myocarditis, immune cells migrate towards the site of infection and secrete proteases, which in turn can act as sheddases by cleaving extracellular domains of transmembrane proteins. We were interested in the shedding of the Coxsackie- and adenovirus receptor (CAR) that acts as an entry receptor for both eponymous viruses, which cause myocarditis. CAR shedding by secreted immune proteases could result in a favourable outcome of myocarditis as CAR’s extracellular domain would be removed from the cardiomyocytes’ surface leading to decreased susceptibility to ongoing viral infections.

Methods and results

In this work, matrix metalloproteinases and serine proteinases were screened for their proteolytic activity towards human CAR. Whereas matrix metalloproteinases, proteinase 3, and cathepsin G did not cleave human recombinant CAR or only within long incubation times, neutrophil elastase showed a distinct cleavage pattern of CAR’s extracellular domain that was time- and dose-dependent. Neutrophil elastase cleaves CAR at its membrane-proximal immunoglobulin domain as we determined by nanoLC-MS/MS. Furthermore, neutrophil elastase treatment of cells reduced CAR surface levels as seen by flow cytometry and immunofluorescence microscopy.

Conclusions

With this study, we show that CAR might be a target for shedding by neutrophil elastase.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11033-022-07153-2.

CVB3 Nonstructural 2A Protein Modulates SREBP1a Signaling via the MEK/ERK Pathway

Coxsackievirus B3 (CVB3) is the predominant pathogen of viral myocarditis. In our previous study, we found that CVB3 caused abnormal lipid accumulation in host cells. However, the underlying mechanisms by which CVB3 disrupts and exploits the host lipid metabolism are not well understood. Sterol regulatory element binding protein 1 (SREBP1) is the major transcriptional factor in lipogenic genes expression. In this study, we demonstrated that CVB3 infection and nonstructural 2A protein upregulated and activated SREBP1a at the transcriptional level. Deletion analysis of SREBP1a promoter revealed that two regions, -1821/-1490 and -312/+217, in this promoter were both required for its activation by 2A. These promoter regions possessed several binding motifs for transcription factor SP1. Next, we used SP1-specific small interfering RNAs (siRNAs) to confirm that SP1 might be the essential factor in SREBP1a upregulation by 2A. Furthermore, we showed that MEK/ERK pathway was involved in the activation of SREBP1a by 2A and that blocking this signaling pathway with the specific inhibitor U0126 attenuated SREBP1a activation and lipid accumulation by 2A. Finally, we showed that inhibition of SREBP1 with siRNAs attenuated lipid accumulation induced by CVB3 infection and reduced virus replication. Moreover, inhibition of the MEK/ERK pathway also led to reduction of SREBP1a activation, lipid accumulation, and virus replication during CVB3 infection. Taken together, these data demonstrate that CVB3 nonstructural 2A protein activates SREBP1a at the transcription level through a mechanism involving MEK/ERK signaling pathway and SP1 transcription factor, which promotes cellular lipid accumulation and benefits virus replication.IMPORTANCE Coxsackievirus B3 (CVB3) infection is the leading cause of viral myocarditis, but effective vaccines and antiviral therapies against CVB3 infection are still lacking. It is important to understand the precise interactions between host and virus for the rational design of effective therapies. During infection, CVB3 disrupts and exploits host lipid metabolism to promote excessive lipid accumulation, which benefits virus replication. SREBP1 is the master regulator of cellular lipid metabolism. Here, we report that one of the viral nonstructural proteins, 2A, upregulates and activates SREBP1a. Furthermore, we find that inhibition of SREBP1 decreases CVB3 virus replication. These results reveal the regulation of SREBP1a expression by 2A and the roles of SREBP1 in lipid accumulation and viral replication during CVB3 infection. Our findings provide a new insight into CVB3 host interactions and inform a potential novel therapeutic target for this important pathogen.

Berberine Restricts Coxsackievirus B Type 3 Replication via Inhibition of c-Jun N-Terminal Kinase (JNK) and p38 MAPK Activation In Vitro

Background

At present, the treatment of coxsackievirus-induced myocarditis remains difficult. Berberine (BBR), an isoquinoline alkaloid isolated from traditional medicine herbs, exhibits significant anti-viral efficacy against various viruses. However, the underlying mechanism by which BBR controls CVB3 infection has not yet been reported. The purpose of this study was to investigate the anti-viral efficacy of BBR against CVB3 infection and its mechanism.

Material/Methods

In our experiments, the protein levels of VP1 and MAPKs signal pathway were measured by Western blot. The mRNA level of VP1 was measured by RT-PCR. The virus titers were determined by TCID₅₀ assay.

Results

We found that BBR treatment significantly decreased CVB3 replication in HeLa cells. In addition, the BBR treatment reduced the phosphorylation levels of JNK and p38 MAPK upon CVB3 infection in both HeLa cells and primary rat myocardial cells.

Conclusions

Taken together, these results suggest that BBR inhibits CVB3 replication through the suppression of JNK and p38 MAPK activation, shedding new light on the investigation of therapeutic strategies against CVB3-induced viral myocarditis.

Activation of AMPK restricts coxsackievirus B3 replication by inhibiting lipid accumulation

Coxsackievirus B3 (CVB3) is the major pathogen of human viral myocarditis. CVB3 has been found to manipulate and modify the cellular lipid metabolism for viral replication. The cellular AMP-activated protein kinase (AMPK) is a key regulator of multiple metabolic pathways, including lipid metabolism. Here we explore the potential roles AMPK plays in CVB3 infection. We found that AMPK is activated by the viral replication during CVB3 infection in Hela cells and primary myocardial cells. RNA interference mediated inhibition of AMPK could increase the CVB3 replication in cells, indicating that AMPK contributed to restricting the viral replication. Next, we showed that CVB3 replication could be inhibited by several different pharmacological AMPK activators including metformin, A769662 and AICAR. And the constitutively active AMPK mutant (CA-AMPK) could also inhibit the CVB3 replication. Furthermore, we found that CVB3 infection increased the cellular lipid levels and showed that the AMPK agonist AICAR both restricted CVB3 replication and reduced lipid accumulation through inhibiting the lipid synthesis associated gene expression. We further found that CVB3 infection would also induce AMPK activated in vivo. The AMPK agonist metformin, which has been widely used in diabetes therapy, could decrease the viral replication and further protect the mice from myocardial histological and functional changes in CVB3 induced myocarditis, and improve the survival rate of infected mice. Lastly, it was demonstrated that the AICAR-mediated restriction of viral replication could be rescued partially by exogenous palmitate, the first product of fatty acid biosynthesis, demonstrating that AMPK activation restricted CVB3 infection through its inhibition of lipid synthesis. Taken together, these data in the present study suggest a model in which AMPK is activated by CVB3 infection and restricts viral replication by inhibiting the cellular lipid accumulation, and inform a potential novel therapeutic strategy for CVB3-associated diseases.